Semiconductive ceramic sintered compact

ABSTRACT

There is provided a semiconductive ceramic sintered compact that has a conductivity high enough to attain static electricity removal and antistatic purposes and, at the same time, has excellent mechanical properties or stability over time. The semiconductive ceramic sintered compact includes at least a main phase and first and second phases contained in the main phase observed as a result of observation of any face of the sintered compact, the main phase being a ceramic sintered phase containing Al 2 O 3  particles, the first phase being a grain boundary phase including a conductive substance-containing conductive phase and Al 2 O 3  particles, the Al 2 O 3  particles being present in an island-sea form in the conductive phase, the second phase being a grain boundary phase containing a conductive phase having the same composition as the conductive phase in the first phase and having a structure that electrically connects the first phases three-dimensionally to each other.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a semiconductive ceramic sinteredcompact that has a conductivity high enough to attain static electricityremoval and antistatic purposes and has excellent mechanical propertiesor stability over time.

2. Background Art

Al₂O₃, ZrO₂, SiC, Si₃N₄ and the like have been extensively used asstructural members for semiconductor manufacturing apparatuses andliquid crystal manufacturing apparatuses by virtue of their excellentmechanical properties, abrasion resistance, and corrosion resistance. Inparticular, Al₂O₃ possesses excellent mechanical properties, abrasionresistance, and corrosion resistance and is low in cost and thus hasbeen used in various portions of apparatuses.

An enhanced performance of semiconductor devices and liquid crystaldevices in recent years has led to further microminiaturization of thesedevices, posing troubles of the devices caused by electrostaticdischarge (ESD) that occurs in guides or the like during drive of stagesin a manufacturing process. Further, static electricity should berapidly released from around the devices. To meet this demand, ceramics,of which the surface resistivity and the volume resistivity have beenlowered by adding conductive substances to alumina that is an insulator,or by using a special sintering method for static electricity removingand antistatic purposes, have hitherto been known (PTLs 1 to 4).

For example, JP 2004-099413 (PTL 4) discloses alumina ceramics that haveantihalation and antistatic functions and have a specific rigidity whichcan maintain a large meter-size mount table with high accuracy. Theceramics include Al₂O₃ and three metal elements of Mn (manganese), Ti(titanium), and Fe (iron) each added in an amount of not less than 0.5%in terms of oxide to Al₂O₃, the total amount of the three elements being2 to 11% in terms of oxide. As long as the present inventors know, theceramics described in this patent publication leave room for animprovement in properties.

CITATION LIST Patent Literature

-   [PTL 1] JP 2008-266069-   [PTL 2] JP 2011-68561-   [PTL 3] JP H09 (1997)-268060-   [PTL 4] JP 2004-099413

SUMMARY OF THE INVENTION Technical Problems

The present inventors have now found that a semiconductive ceramicsintered compact including at least a main phase containing Al₂O₃particles and a phase that is present in the main phase and includes aconductive phase containing a conductive substance, the phases havingrespective specific structures that are mutually related, has excellentvarious properties, specifically a conductivity high enough to attainstatic electricity removal or antistatic purposes and has excellentmechanical properties or stability over time.

Accordingly, an object of the present invention is to provide asemiconductive ceramic sintered compact having excellent variousproperties, particularly a semiconductive ceramic sintered compact thathas a conductivity high enough to attain static electricity removal orantistatic purposes and, at the same time, has excellent mechanicalproperties or stability over time.

Solution to Problems

According to the present invention, there is provided a semiconductiveceramic sintered compact comprising:

at least a main phase and first and second phases contained in the mainphase observed as a result of observation of any face of the sinteredcompact, wherein

the main phase is a ceramic sintered phase comprising Al₂O₃ particles,

the first phase is a grain boundary phase comprising a conductivesubstance-containing conductive phase and Al₂O₃ particles, and the Al₂O₃particles is present in an island-sea form in the conductive phase,

the second phase is a grain boundary phase containing a conductive phasehaving the same composition as the conductive phase in the first phaseand having a structure that electrically connects the first phasesthree-dimensionally to each other.

Effects of the Invention

The present invention provides a semiconductive ceramic sintered compactthat has a conductivity high enough to attain static electricity removalor antistatic purposes and, at the same time, has excellent mechanicalproperties or stability over time. The provision of the abovesemiconductive ceramic sintered compact can contribute to thesuppression of ESD that is a problem involved in liquid crystalmanufacturing apparatuses, semiconductor manufacturing apparatuses andthe like and can meet microminiaturization and increase in size ofdevices. Further, according to the present invention, the sinteredcompact can be densified by sintering at ordinary atmospheric pressure,and, thus, homogeneous and low-cost dense sintered compacts can beprepared, offering an advantage that the sintered compact does notundergo a change in accuracy of planar parallelism over time.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an image photographed under a laser microscope showing amicrostructure of a semiconductive ceramic sintered compact according tothe present invention prepared in Example 1.

FIG. 2 is an image that has been photographed under SEM (a scanningelectron microscope) and corresponds to an enlarged image of FIG. 1.

FIG. 3 is an image that has been photographed under EFM and shows aconductive path of a semiconductive ceramic sintered compact accordingto the present invention prepared in Example 1.

FIG. 4 is an image obtained by a compositional analysis of asemiconductive ceramic sintered compact according to the presentinvention prepared in Example 1.

FIG. 5 is a profile determined by XRD (X-ray diffractometry) of asemiconductive ceramic sintered compact according to the presentinvention prepared in Example 7.

FIG. 6 is a profile determined by XRD (X-ray diffractometry) of asemiconductive ceramic sintered compact according to the presentinvention prepared in Example 13.

DESCRIPTION OF EMBODIMENTS

The semiconductive ceramic sintered compact according to the presentinvention will be described.

Semiconductive Ceramic Sintered Compact

The semiconductive ceramic sintered compact according to the presentinvention includes: at least a main phase and first and second phasescontained in the main phase observed as a result of observation of anyface of the sintered compact, the main phase being a ceramic sinteredphase including Al₂O₃ particles, the first phase being a grain boundaryphase including a conductive substance-containing conductive phase andAl₂O₃ particles, the Al₂O₃ particles being present in an island-sea formin the conductive phase, the second phase being a grain boundary phasecontaining a conductive phase having the same composition as theconductive phase in the first phase and having a structure thatelectrically connects the first phases three-dimensionally to eachother. When the semiconductive ceramic sintered compact according to thepresent invention takes this structure, portions where Al₂O₃ particlesprepare necks are formed. Consequently, a conductive path is formed froma relative small amount of the conductive phase. Further, mechanicalproperties of the sintered compact are improved.

First Phase

The first phase is a grain boundary phase that is present in the mainphase and includes a conductive substance-containing conductive phaseand Al₂O₃ particles, the Al₂O₃ particles being present in an island-seaform in the conductive phase. Specifically, the first phase is a phasepresent in a center portion of FIG. 1. In FIG. 1, a light gray portionis the conductive phase, and a dark gray portion present like islands inthe conductive phase is Al₂O₃ particles. Accordingly, the term“island-sea” as used herein means such a state that dispersed phases(island component) are dispersed in a continuous phase (sea component).The sea component is a conductive phase including a conductivesubstance, and the island component is Al₂O₃ particles.

Second Phase

The second phase is a grain boundary phase that is present in the mainphase including Al₂O₃ particles, has a conductive phase having the samecomposition as the conductive phase in the first phase and has astructure that electrically connects the first phasesthree-dimensionally to each other. The conductive phase has an ant'snest-like distribution. When any face of the sintered compact accordingto the present invention is observed, a three-dimensionally thin portionin the conductive phase has a distribution as in the second phase and isseen as discrete spots. A light gray portion present as spots in a phasewhich is shown as a dark gray portion in FIG. 1 and in which Al₂O₃particles are bound to each other is a conductive phase. A gray portionintermediate between the light gray portion and the dark dray portion isa glass phase formed of SiO₂.

Preferably, the semiconductive ceramic sintered compact in oneembodiment according to the present invention has a conductive phasecontaining Fe (iron) and Ti (titanium). When Fe and Ti are contained, aconductivity high enough to attain static electricity removal andantistatic purposes can be developed in a small addition amount.

In the semiconductive ceramic sintered compact in one embodiment of thepresent invention, preferably, the conductive phase further contains Mn(manganese). When Mn is contained, effective conductivity is developedand the sintered compact is densified.

In the semiconductive ceramic sintered compact in one embodiment of thepresent invention, preferably, the conductive phase contains Mn and Ti.When Mn and Ti are contained, a conductivity high enough to attainstatic electricity removal and antistatic purposes is developed in asmall addition amount.

In the semiconductive ceramic sintered compact in one embodiment of thepresent invention, preferably, the conductive phase contains crystalshaving an ilmenite structure. In addition to ilmenite crystals, spinelcrystals are also precipitated. Crystals having an ilmenite structureare dominant as the crystal phase contributed to the conductivity of thesemiconductive ceramic sintered compact according to the presentinvention. Further, although a plurality of compounds having an ilmenitestructure are present, the precipitation of FeTiO₃, MnTiO₃, orMn_(x)Fe_(1-x)TiO₃ compounds is preferred.

Further, in the semiconductive ceramic sintered compact accoding to oneembodiment of the present invention, preferably, when the semiconductiveceramic sintered compact is pulverized and mixed with 1% by weight of aSi (silicon) powder having a purity of 99.9999% or more is analyzed byX-ray diffractometry, a value obtained by dividing a peak area at 32° bya peak area at 28° and multiplying the obtained value by 100 is not lessthan 40. Depending upon the state of measurement and specimens,measurement sample fixation methods, and crystallinity of the sinteredcompact, the position of peaks detected is sometimes shifted at around32° and 28°. In this case, the peak area may be obtained in the shiftedpeak. In the present invention, a conductivity derived from the crystalshaving an ilmenite structure is dominant, and effective conductivity isdeveloped when the peak area ratio is not less than 40.

Preferably, the semiconductive ceramic sintered compact in oneembodiment of the present invention satisfies that, in a microstructureimage obtained by photographing the semiconductive ceramic sinteredcompact with a laser microscope or an electron microscope, the area ofthe conductive phase relative to the area of the main phase includingAl₂O₃ particles is 0% (exclusive) to 15% (inclusive), and the conductivephase contains two or more metals selected from Mn, Fe, and Ti and has acomposition satisfying a relation of Mn/(Ti+Mn+Fe)>0.08 or Mn/Ti>0.15.The area of the conductive phase is more preferably 0% (exclusive) to10% (inclusive), still more preferably 0.5% (exclusive) to 4%(inclusive). When the area of the conductive phase is not more than 15%,a good balance between the conductivity and the mechanical properties ofthe ceramic sintered compact can be obtained. The proportion of thecomponents in the conductive phase meets a relation ofMn/(Ti+Mn+Fe)>0.08 or Mn/Ti>0.15, preferably Mn/(Ti+Mn+Fe)>0.1 orMn/Ti>0.2, more preferably Mn/(Ti+Mn+Fe)>0.15 or Mn/Ti>0.25. When thecomponent ratio meets a relation of Mn/(Ti+Mn+Fe)>0.08 or Mn/Ti>0.15, aconductivity high enough to attain static electricity removal orantistatic purposes is developed and the sintered compact is densified.“Proportion of the components in the conductive phase” means the ratioof presence of individual elements (number of individual elements)obtained by an elementary analysis (=atomic %), for example, by energydispersive X-ray fluorescence diffractometry (EDX).

In the semiconductive ceramic sintered compact in one embodiment of thepresent invention, when the conductive phase contains crystals having anilmenite structure, the following requirements are satisfied: the areaof the conductive phase is 10% (exclusive) to 15% (inclusive); theconductive phase contains two or more metals selected from Mn, Fe, andTi; and the proportion of the components in the conductive phase meets arelation of Mn/(Ti+Mn+Fe)>0.08 or Mn/Ti>0.15.

In the semiconductive ceramic sintered compact in one embodiment of thepresent invention, the surface resistivity is preferably not more than10¹³ [Ω/sq.], more preferably 10⁵ [Ω/sq.] to 10¹³ [Ω/sq.], still morepreferably 10⁷ [Ω/sq.] to 10¹³ [Ω/sq.]. When the surface resistivity isnot less than 10⁵ Ω/sq., instantaneous neutralization of chargeselectrified to materials is prevented and, consequently, the possibilityof disadvantageously generating discharge can be suppressed. When thesurface resistivity is not more than 10¹³ Ω/sq., it is possible toprevent the material from being brought to a state close to an insulatorand to prevent charges from staying in the material.

In the semiconductive ceramic sintered compact in one embodiment of thepresent invention, preferably, the specific rigidity is not less than 60[GPa], more preferably not less than 70 [GPa]. When the specificrigidity is not less than 60 [GPa], the flexibility of the structure isnot increased and the accuracy required of the sintered compact can beobtained.

In the semiconductive ceramic sintered compact in one embodiment of thepresent invention, the water absorption coefficient is preferably notmore than 0.1%, more preferably not more than 0.05%. When the waterabsorption coefficient is not more than 0.1%, the accuracy required ofthe sintered compact can be obtained.

When both the first and second phases are considered in terms ofconductivity and are understood without distinction from each other, thesemiconductive ceramic sintered compact according to the presentinvention can be understood as one that includes a main phase includingAl₂O₃ particles and a grain boundary phase present between the mainphases, the grain boundary phase including conductive crystals having anilmenite structure as a conductive phase.

Thus, according to another aspect of the present invention, there isprovided a semiconductive ceramic sintered compact including: a mainphase including Al₂O₃ particles; and a grain boundary phase presentbetween the main phases, the grain boundary phase including conductivecrystals having an ilmenite structure as a conductive phase. All ofmatters (for example, proportion of the components and area of theconductive phase, crystals having an ilmenite structure, surfaceresistivity of ceramic sintered compact, specific rigidity, and waterabsorption coefficient) described above in connection with thesemiconductive ceramic sintered compact according to the above aspect ofthe present invention are true of the semiconductive ceramic sinteredcompact according to this aspect of the present invention. Preferably,the semiconductive ceramic sintered compact including crystals having anilmenite structure as the conductive phase in this aspect meets thefollowing requirements: the area of the conductive phase is 0%(exclusive) to 10% (inclusive): the conductive phase include two or moremetals selected from Mn, Fe, and Ti; and the proportion of thecomponents in the conductive phase meets a relation ofMn/(Ti+Mn+Fe)>0.08 or Mn/Ti>0.15. When the semiconductive ceramicsintered compact including crystals having an ilmenite structure as theconductive phase meets the requirements, the semiconductive ceramicsintered compact has a conductivity high enough to attain staticelectricity removal and antistatic purposes, excellent mechanicalstrength or stability over time, and, at the same time, can ensure agood balance between the conductivity and the mechanical properties. Inparticular, excellent mechanical strength or stability over time can berealized. Further, in the semiconductive ceramic sintered compactaccording to one embodiment of the present invention, the area of theconductive phase is 10% (exclusive) to 15% (inclusive). This sinteredcompact also exerts practically desired effects although there is apossibility that downturn in an improvement in some of performance andproperties occurs.

By virtue of excellent static electricity removing or antistaticproperties and mechanical properties or stability over time, thesemiconductive ceramic sintered compact according to the presentinvention can be advantageously used, for example, in structural membersused in semiconductor manufacturing apparatuses or liquid crystalmanufacturing apparatuses (more specifically stages in semiconductordevice or liquid crystal manufacturing apparatuses, and drive guides),and various mechanical components, tools, guides and the like that arerequired to have mechanical properties and have complicated shapesrequired to be machined by electric discharge.

Manufacturing Method

The method for manufacturing a semiconductive ceramic sintered compactaccording to the present invention will be described. For MnO₂, Fe₂O₃,and TiO₂ that are starting materials for the conductive substance,preferably, the three starting materials have a purity of not less than95% and have a mean particle diameter of not more than 5 μm, morepreferably not more than 3 μm, still more preferably not more than 1 μm.For a sintering mechanism of the semiconductive ceramic sintered compactaccording to the present invention, liquid phase sintering is preferred,and, in a mean particle diameter of more than 5 μm, the conductivesubstance portion, when converted to a liquid phase, allows the liquidphase to be diffused into the molded product to form residual pores. Thetotal addition amount of the three starting materials is preferably notmore than 25% by weight, more preferably not more than 23% by weight,still more preferably not more than 21% by weight. When the totaladdition amount is not more than 25% by weight, the mechanicalproperties are not lowered and, at the same time, a difference incoefficient of thermal expansion between the conductive phase and Al₂O₃as the main phase can eliminate a possibility of the occurrence ofresidual stress or cracking.

SiO₂ may be added as a sintering aid. Preferably, SiO₂ has a meanparticle diameter of not more than 5 μm. The mean particle diameter ismore preferably not more than 3 μm, still more preferably not more than1 μm. When the mean particle diameter is not more than 5 μm, as with theconductive substance, SiO₂ also constitutes a liquid phase componentand, thus, there is no possibility of occurrence of pores. The additionamount is preferably not more than 10% by weight, more preferably notmore than 8% by weight, still more preferably not more than 6% byweight. When the addition amount is not more than 10% by weight, themechanical properties are not lowered and a difference in coefficient ofthermal expansion between the conductive phase and Al₂O₃ as the mainphase can allow the occurrence of residual stress and cracking to besuppressed.

In a preferred embodiment of the present invention, preferably, theAl₂O₃ starting material for constituting the main phase has a purity ofnot less than 95%. The addition amount is a value (a balance) obtainedby subtracting the amount of the conductive substance starting materialand the amount of the SiO₂ starting material as the sintering aid fromthe composition. The use of two types of Al₂O₃ starting materials havingmutually different mean particle diameter is preferred. For example, anAl₂O₃ starting material having a mean particle diameter of not less than2 μm and an Al₂O₃ starting material having a mean particle diameter ofnot more than 1 μm may be used. The use of an Al₂O₃ starting materialhaving a larger mean particle diameter of not less than 2 μm and anAl₂O₃ starting material having a smaller mean particle diameter of notmore than 1 μm can contribute to an improved volume packing ratio of thesolid content in the molded product and can realize excellent staticelectricity removing or antistatic properties in a small proportion ofthe conductive phase. The addition ratio between the Al₂O₃ startingmaterial having a larger mean particle diameter and the Al₂O₃ startingmaterial having a smaller mean particle diameter is that preferably notless than 50%, more preferably not less than 70%, still more preferablynot less than 90%, of the total amount of Al₂O₃ is accounted for by theAl₂O₃ starting material having a larger mean particle diameter. When theaddition ratio of the Al₂O₃ starting material having a larger meanparticle diameter is not less than 50%, advantageously, the packingratio in the molded product can be improved and, further, the Al₂O₃particles having a smaller mean particle diameter start sintering at alow temperature, whereby pores that are deemed to derive from aheterogeneous conductive phase can also be suppressed.

Preferably, these starting materials, a solvent, and a dispersant areadded and ground and mixed in a ball mill, and the mixture is granulatedwith a spray dryer or the like. In the grinding and mixing, desirably,the conductive substance, the sintering aid, and the Al₂O₃ startingmaterial having a smaller particle diameter are firstly introducedfollowed by preliminary grinding. This method can facilitate theformation of a conductive phase having a homogeneous composition.Preferably, the prepared granulated powder is subjected to pressing andCIP molding to prepare a molded product. Alternatively, the moldedproduct may be prepared by casting or extrusion. The molded product maybe sintered in the atmospheric environment by holding the molded productat a maximum temperature of 1200 to 1500° C. for 1 to 10 hr. Sinteringin the atmospheric environment is preferred. The sintering in theatmospheric environment may be carried out in any of an electric furnaceand a furnace using a fuel such as LPG.

EXAMPLES

For starting materials in Examples 1 to 13 and Comparative Examples 1and 2, 2.1 to 9.0% by weight of a commercially available MnO₂ startingmaterial having a mean particle diameter of 5 μm, 2.1 to 9.0% by weightof a commercially available Fe₂O₃ starting material having a meanparticle diameter of 2 μm, and 0.7 to 4.5% by weight of a commerciallyavailable TiO₂ starting material having a mean particle diameter of 0.5μm were added as conductive substances, 2 to 6% by weight of a SiO₂starting material having a mean particle diameter of 2 μm was added as asintering aid, and a commercially available Al₂O₃ starting materialhaving a mean particle diameter of 0.5 μm and a commercially availableAl₂O₃ starting material having a mean particle diameter of 3 μm wereadded as the balance. For starting materials in Comparative Example 3,in addition to the above starting materials, 0.4% by weight of a MgOstarting material having a mean particle diameter of 2 μm and 0.7% byweight of a CaO starting material having a mean particle diameter of 5μm were added.

The starting materials, ion-exchanged water, and a dispersant(polycarboxylic ammonium) were placed in a ball mill and were ground andmixed for 20 hr. An acrylic binder was added and mixed therewith for afew minutes, and the slurry was taken out and deaerated. The deaeratedslurry was cast into a plaster mold that can provide a green body havinga size of 100 mm square and a thickness of 10 mm, followed by thepreparation of a green body. The surface layer of the demolded and driedgreen body was polished with an abrasive material of #80, and polishedgreen body was atmospherically sintered at 1300 to 1450° C. The sinteredproducts thus prepared were subjected to the measurement of the arearatio of a conductive phase in a sintered compact under a lasermicroscope, a compositional analysis of a conductive phase in a sinteredcompact under SEM, identification of a crystal phase (measurement ofarea ratio relative to Si (silicon) in an ilmenite crystal phase) in asintered compact with an X-ray diffraction apparatus, the measurement ofsurface resistivity, the measurement of specific rigidity, and themeasurement of water absorption coefficient by the following evaluationmethods. The results of evaluation are shown in Table 1.

Evaluation Test

Area Ratio of Conductive Phase in Sintered Compact

The analysis for the determination of the area ratio of the conductivephase in the sintered compact was carried out under a laser microscope.OLS4000 manufactured by Shimadzu Seisakusho Ltd. was used as the lasermicroscope. The observation was made in an area of 480 μm×480 μm, and abrightness image in this area was photographed. The conductive phasecontains a transition metal and thus exhibits a high brightness, and,thus, a high-brightness portion can be separated as the conductive phaseby an image analysis. Win ROOF V6.5 was used for the image analysis.Images obtained under the laser microscope were monochromated, theconductive phase was separated by digitization at a monochromaticthreshold of 170 to 210 to determine the area ratio. The area ratio wasdetermined as a proportion of the area of the conductive phase to thetotal area excluding the area of a pore portion. Regarding conditionsfor the preparation of samples, mirror polishing was adopted as in theobservation under EFM.

Compositional Analysis of Conductive Phase in Sintered Compacts

The composition of the conductive phase in the sintered compact wasanalyzed under a scanning electron microscope. Quanta250 manufactured byFEI was used as the scanning electron microscope. Regarding measurementconditions, SEM observation (SE and BE) was made under conditions of anaccelerated voltage of 10 kV, a working distance of 10 mm, a spot of 4,and a magnification of 2000 times, and EDS analysis was carried outunder conditions of an accelerated voltage of 10 kV, a working distanceof 10 mm, a spot of 7, a magnification of 2000 times, a number of pixelsof 256×220, a frame time of 2000, a rate of 4, and a drift correctionzoom coefficient of 2. An analysis software NORAN SYSTEM7 manufacturedby Thermo Fisher Scientific was used for the compositional analysis ofthe conductive phase. Images photographed at the above magnification wassubjected to an elemental mapping analysis. Phases were separated basedon the component ratio and the component ratio of the phasecorresponding to the conductive phase was obtained. Regarding conditionsfor the preparation of samples, mirror polishing was performed in thesame manner as in the observation under EFM, followed by platinum vapordeposition to prepare samples.

Method for Identifying Crystal Phase in Sintered Compact

The identification of the crystal phase in the sintered compacts wascarried out with an X-ray diffractometer. X'PertPRO manufactured byPANalytical was used as the X-ray diffractometer. The intensity of peaksof each of the sintered compacts by X-ray diffractometry was measuredunder conditions of X-ray output (CuKα radiation) of 45 kV and 40 mA, ascanning range of 27° to 34°, a scanning speed of 0.005°/sec, and ascanning time of 1 sec/0.005°. For a relative comparison of peakintensity, 1% by weight of a high-purity metal silicon powder (purity99.9999%) was physically mixed with each sample. A peak area X wascalculated from a peak intensity attributable to a (111) face of themeasured metallic silicon and a half-value width of the peak, a peakarea Y was calculated from a peak intensity attributable to a (104) faceof ilmenite and a half value width of the peak, and a relative arearatio was determined by multiplying Y/X by 100. The maximum peak heightaround each peak angle was regarded as each peak intensity.

Method for Measuring Surface Resistivity

The surface resistivity was measured with Highrester UP (MCP-HT450)manufactured by Mitsubishi Chemical Co., Ltd. The measurement was madeunder an environment of a measurement temperature of 23±1° C. and ahumidity of not more than 50%. A UR probe (MCP-HTP12) was used as theprobe for the probe measurement. Regarding measurement conditions, anapplied voltage of 1000 V was adopted, and, after the application, 60sec elapsed until a stable surface resistivity was obtained, and thestable surface resistivity was regarded as the surface resistivity. Thesurface resistivity was measured twice in total for obverse and reversesides of the samples, the measured values were averaged, and the averagevalue was regarded as the surface resistivity of the sintered compact.Regarding conditions for the preparation of samples, a thickness of 1 mmfrom the surface of the sintered compact was removed by grinding with agrinding stone of #80 for sample preparation.

Specific Rigidity

Young's modulus was measured by a resonance method, and specific gravitywas measured by an Archimedes method. The specific rigidity wascalculated by dividing the Young's modulus by the specific gravity.JE-RT3 manufactured by Nihon Techno-Plus Co., Ltd was used in themeasurement of the Young's modulus. In the measurement of the specificgravity by the Archimedes method, CP224S manufactured by Sartorius wasused as a balance.

Water Absorption Coefficient

The water absorption coefficient was calculated from the dry weightmeasured by the Archimedes method, the weight in water, and watersaturated weight (a weight of the sample subjected to the measurement ofthe weight in water after wiping with a dry cloth; when open pores arepresent, the weight is larger than the dry weight), that is, wascalculated by subtracting the dry weight from the water saturatedweight, dividing the obtained value by the dry weight, and multiplyingthe obtained value by 100.

TABLE 1 Starting materials Conductive Al₂O₃ [%] Other than Al₂O₃ phase0.5 μm 3 μm MnO₂ Fe₂O₃ TiO₂ SiO₂ MgO CaO Total [Area %] Example 1 87.00.0 5.0 3.0 3.0 2.0 — — 13.0 2.57 Example 2 81.0 0.0 7.5 4.5 4.5 2.0 — —18.5 3.87 Example 3 58.1 24.9 5.0 3.0 3.0 6.0 — — 17.0 1.48 Example 460.4 25.9 3.5 2.1 2.1 6.0 — — 13.7 1.25 Example 5 77.7 8.6 3.5 2.1 2.16.0 — — 13.7 1.92 Example 6 74.7 8.3 5.0 3.0 3.0 6.0 — — 17.0 3.25Example 7 26.1 60.9 3.0 3.0 1.0 6.0 — — 13.0 1.63 Example 8 9.1 82.0 2.12.1 0.7 4.0 — — 8.9 1.58 Example 9 26.7 62.4 2.1 2.1 0.7 6.0 — — 10.91.18 Example 10 8.7 78.3 3.0 3.0 1.0 6.0 — — 13.0 2.33 Example 11 22.552.5 9.0 9.0 3.0 4.0 — — 25.0 13.87 Example 12 24.6 57.4 6.0 6.0 2.0 4.0— — 18.0 10.53 Example 13 25.7 59.9 4.5 4.5 1.5 4.0 — — 14.5 5.02Comparative 93.0 0.0 1.0 3.0 1.0 2.0 — — 7.0 0.00 Example 1 Comparative87.0 0.0 1.0 5.0 3.0 4.0 — — 13.0 0.00 Example 2 Comparative 62.0 26.61.3 2.0 1.1 6.0 0.4 0.7 10.4 2.15 Example 3 Ilmenite Component ratio ofcrystal log conductive phase phase (surface Specific Water Mn/ Arearesistivity) rigidity absorption (Mn + Fe + Ti) Mn/Ti ratio to Si [Ω/sq][GPa] [%] Example 1 0.24 0.49 134.6 12.29 71.0 0.011 Example 2 0.23 0.53134.9 11.43 68.1 0.013 Example 3 0.17 0.32 207.4 11.49 73.5 0.008Example 4 0.22 0.47 50.27 12.11 74.8 0.014 Example 5 0.25 0.49 50.1912.05 74.5 0.015 Example 6 0.19 0.39 50.16 11.86 73.7 0.001 Example 70.24 0.61 48.14 11.95 77.3 0.012 Example 8 0.40 1.12 49.34 11.26 84.80.012 Example 9 0.41 1.29 50.73 11.10 77.0 0.021 Example 10 0.20 0.4748.50 11.16 78.7 0.009 Example 11 0.12 0.28 96.39 11.01 67.1 0.012Example 12 0.12 0.31 80.53 10.84 72.5 0.011 Example 13 0.12 0.31 70.0812.47 76.2 0.088 Comparative 0.07 0.12 0.00 14.25 81.4 0.011 Example 1Comparative 0.08 0.15 0.00 14.06 70.2 0.010 Example 2 Comparative 0.070.08 0.00 12.39 71.5 0.181 Example 3

In Examples 1 to 13, a crystal structure of ilmenite type wasprecipitated, the area of the conductive phase was 0% (exclusive) to 15%(inclusive), and the component ratio of the conductive phase wasMn/(Ti+Mn+Fe)>0.08 and Mn/Ti>0.15. The conductivity was expressed interms of the area of the conductive phase. When look at athree-dimensional standpoint, the conductive phase was present in aproportion of 5 to 22% by volume. In all the Examples, semiconductiveceramic sintered compacts having excellent surface resistivity, specificrigidity, and water absorption coefficient could be produced.

Imaging by Laser Microscope, SEM, EFM, and XRD

For Examples 1, 7, and 13, imaging was carried out by a lasermicroscope, SEM, EFM, and XRD.

FIG. 1 is an image of a microstructure in Example 1 that has beenphotographed under a laser microscope and includes a first phase and asecond phase, wherein the first phase includes a conductive phase formedof a conductive substance and Al₂O₃ particles present in an island-seaform in the conductive phase and the second phase includes a conductivephase that has the same composition as the first phase present in themain phase formed of Al₂O₃ particles and has a structure whichthree-dimensionally connects the first phases to each other.

FIG. 2 is an enlarged image of FIG. 1 that has been photographed underSEM and shows a structure of the first phase.

FIG. 3 is an image under EFM that shows such a state that electricityflows into the microstructure shown in FIG. 2. The image was observed bythe following method.

Observation Under EFM

The conductive phase in the sintered compact was visualized under anelectrical force microscope (EFM). The conductive phase in the presentinvention refers to a phase that allows charges to be transferred withinthe semiconductive ceramic sintered compact and can be observed as aleakage electric field gradient image using an electrical forcemicroscope mode of an atomic force microscope (AFM). AFM manufactured byBruker (D-3100 manufactured by DI) was used as the electrical forcemicroscope. The observation was made in an area of 65 μm×65 μm underconditions of Analog2-6 V, a scan rate of 0.8 Hz, and a lift scan heightof 1 nm. Samples were prepared by subjecting the sintered compact tomirror polishing by buffing with abrasive grains having a particlediameter of 1 μm by an automatic polishing machine manufactured byBUEHLER and ultrasonically cleaning the polished sintered compact withacetone.

FIG. 4 is an image obtained by subjecting the image shown in FIG. 2 tomapping for each component by energy dispersive X-ray fluorescencespectrometry (EDX). From the mapping, it is apparent that the area ofthe conductive phase relative to the main phase formed of Al₂O₃particles is 0% (exclusive) to 15% (inclusive), two or more of Mn, Fe,and Ti were contained in the conductive phase, and the composition ofthe conductive phase satisfies a relation of Mn/(Ti+Mn+Fe)>0.08 orMn/Ti>0.15. Images of individual phases (phases 1 to 6) shown in FIG. 4will be described below, and the component ratio of the individualphases is shown in Table 2 below.

Phase 1: Phase composed of Fe-containing alumina

Phase 2: Phase that constitutes an ilmenite phase composed of Fe, Mn andTi and contributes to conductivity.

Phase 3: Mn-rich phase

Phase 4: Phase that constitutes a spinel of Mn, Fe and also contributesto conductivity.

Phase 5: Ti-rich phase

Phase 6: Phase composed of Mn-containing alumina.

TABLE 2 Name of element Concentration of atom [%] radiation Phase 1Phase 2 Phase 3 Phase 4 Phase 5 Phase 6 C K 1.8 1.46 1.88 2.01 1.42 6 OK58.46 57.13 57.07 52.03 54.85 44.02 F K 0 0.12 0 0.41 0.78 0 Na K 0 00.52 0 0.1 0 Al K 37.22 17.41 22.42 22.29 14.22 44.86 Si K 0.24 0.2 9.360.53 0.85 0.92 SK 0 0 0.02 0 0 0 Ca K 0 0 0.1 0 0 0 Ti K 0.28 11.17 1.080.89 11.03 0.49 Mn K 0.5 5.51 6.02 14.63 13 1.46 Fe L 1.03 6.44 1.19 6.73.2 0.91 Cu L 0 0 0 0 0 0.61 Ge L 0 0.04 0 0 0.04 0 ZrL 0.33 0.32 0 0.320.33 0.51 Pt M 0.13 0.19 0.35 0.19 0.18 0.21 Pb M 0 0.01 0 0 0 0.02 Ti M0.02 0 0 0 0 0 Total 100 100 100 100 100 100

FIG. 5 is a graph showing the results of measurement by powder X-raydiffractometry of a sample obtained by pulverizing the semiconductiveceramic sintered compact in Example 7, adding 1% by weight of a Sipowder having a purity of 99.9999% or more to the powder, and mixingthem together. A value obtained by dividing the peak area at 32° by thepeak area at 28° and multiplying the obtained value by 100 is not lessthan 40.

FIG. 6 is a graph showing the results of measurement by powder X-raydiffractometry of a sample obtained by pulverizing the semiconductiveceramic sintered compact in Example 13, adding 1% by weight of a Sipowder having a purity of 99.9999% or more to the powder, and mixingthem together. A value obtained by dividing the peak area at 32° by thepeak area at 28° and multiplying the obtained value by 100 is not lessthan 40.

For Comparative Examples 1 and 2, the ilmenite crystal phase was notprecipitated, the composition of the conductive phase did satisfyneither Mn/(Ti+Mn+Fe)>0.08 nor Mn/Ti>0.15, and the surface resistivitywas high and poor. For Comparative Example 3, the ilmenite crystal phasewas not precipitated, the composition of the conductive phase didsatisfy neither Mn/(Ti+Mn+Fe)>0.08 nor Mn/Ti>0.15, and the waterabsorption coefficient was high and poor.

What is claimed is:
 1. A semiconductive ceramic sintered compactcomprising: a main phase and first and second phases contained in themain phase observed as a result of observation of any face of thesintered compact, wherein the main phase is a ceramic sintered phasecomprising Al₂O₃ particles, the first phase is a grain boundary phasecomprising a conductive substance-containing conductive phase and Al₂O₃particles, and the Al₂O₃ particles is present in an island-sea form inthe conductive phase, and the second phase is a grain boundary phasecontaining a conductive phase having the same composition as theconductive phase in the first phase and having a structure thatelectrically connects the first phases three-dimensionally to eachother, wherein the semiconductive ceramic sintered compact comprisesSiO₂, wherein the conductive phase contains Fe (iron) and Ti (titanium),wherein the conductive phase contains crystals having an ilmenitestructure, wherein the semiconductive ceramic sintered compact has avalue not less than 40 according to a powdery X-ray diffractometry, andthe value is obtained by, when a powder of the semiconductive ceramicsintered compact mixed with 1% of a Si (silicon) powder having a purityof 99.9999% or more is analyzed by the powdery X-ray diffractometry, apeak area at 32° is divided by a peak area at 28° and then multiplied by100.
 2. The semiconductive ceramic sintered compact according to claim1, wherein the conductive phase further contains Mn (manganese).
 3. Thesemiconductive ceramic sintered compact according to claim 1, whereinthe conductive phase contains Mn and Ti.
 4. The semiconductive ceramicsintered compact according to claim 1, wherein, in a microstructureimage obtained by photographing the semiconductive ceramic sinteredcompact with a laser microscope or an electron microscope, the area ofthe conductive phase relative to the area of the main phase comprisingAl₂O₃ particles is 0% (exclusive) to 15% (inclusive), and the conductivephase contains two or more metals selected from Mn, Fe, and Ti and has acomposition satisfying a relation of Mn/(Ti+Mn+Fe)>0.08 or Mn/Ti>0.15.5. The semiconductive ceramic sintered compact according to claim 1,which has a surface resistivity of not more than 10¹³ [Ω/sq.].
 6. Thesemiconductive ceramic sintered compact according to claim 1, which hasa specific modulus of rigidity of not less than 60 [GPa].
 7. Thesemiconductive ceramic sintered compact according to claim 1, which hasa water absorption coefficient of not more than 0.1%.
 8. A structuralmember for a liquid crystal or semiconductor manufacturing apparatus,the structural member being formed of a semiconductive ceramic sinteredcompact according to claim
 1. 9. The semiconductive ceramic sinteredcompact according to claim 1, wherein the amount of SiO2 is not morethan 10% by weight.
 10. The semiconductive ceramic sintered compactaccording to claim 1, wherein the amount of SiO2 is not more than 8% byweight.
 11. The semiconductive ceramic sintered compact according toclaim 1, wherein the amount of SiO2 is not more than 6% by weight. 12.The semiconductive ceramic sintered compact according to claim 1,wherein semiconductive ceramic sintered compact is prepared by sinteringin the atmospheric environment.
 13. The semiconductive ceramic sinteredcompact according to claim 1, wherein the surface resistivity ismeasured under an environment of a measurement temperature of 23+/−1° C.and a humidity of not more than 50%.